The present invention relates generally to a printing system and, more particularly, to a continuous label printing system utilizing a sheet printer.
Generally, labels are printed by a continuous printing process utilizing a roll label print media. Generally the continuous process for printing labels has been reserved to the flexographic, gravure and thermal printing processes.
Flexographic printing, also known as aniline printing, is a form of relief printing in which a slightly raised image of the label is formed on a printing plate by engraving. In flexographic printing, the raised image is inked and the ink is transferred directly to the print media, typically by a large rotary press. Color labels are printed by passing the print media through the system multiple times. In a four color printing process, the print media is passed through the system four times, once for each of black, cyan, magenta and yellow. Each plate has a high initial cost and has a limited life, requiring periodic replacement. While flexographic systems are efficient at printing very high volumes of labels and/or other documents, flexographic systems also require extensive set-up time (i.e. engraving and replacing the plates) making it cost prohibitive for small runs. Further, flexographic systems are also very large and expensive to purchase. Generally, a print run must be on the order of millions of labels in order for the print run to be cost effective.
Another process for printing labels is known as gravure or rotogravure printing. In gravure printing, the printing area is etched into a surface of a plate or a metal cylinder. In contrast to flexographic printing, the etched out sections are filled with ink and the excess ink on the non-image area is removed by a thin stainless steel blade referred to as a doctor blade. The size and depth of the etched out areas determine how much ink is deposited on the print media. Gravure etched cylinders can cost thousands of dollars. Generally, a print run for a gravure system is on the order of millions of copies in order to be cost effective. Thus, gravure systems suffer from the same drawbacks for a short print run as do flexographic systems.
Thermal printing is a non-impact printing process that uses heat to register an impression on paper. A typical thermal transfer printer has a print head containing many small resistive heating pins that on contact, either melt wax-based ink onto ordinary media or burn dots onto specially coated media. Similar to flexographic printing, thermal printing is usually accomplished through a multi-pass process wherein each color is applied separately. However, thermal-transfer printing systems are not bound by the limits of a printing plate and can rapidly change the image being printed. The major drawback to thermal printing compared to flexographic and gravure printing, is the relatively low quality of the printed image, especially on print media that is not specialty paper. Further, thermal printing equipment is also very expensive to purchase and to maintain as the print heads must be cleaned frequently to remove melted wax or burned-on ink.
What is needed but not provided by the prior art, is a continuous label printing system that allows for just-in-time printing of variable information color images, text and bar codes in small batches without the need for engraved printing plates such as used on flexographic and gravure printing, and which provides a quality equivalent to flexographic and gravure printing. Further, the continuous label printing system should be capable of utilizing print media from a roll and provide the printed-on media in a roll.